Known in the art are sequencers which operate autonomously with only condition codes to control program flow. One such sequencer is manufactured as an integrated circuit by Advanced Micro Devices, Inc. and designated the Am29PL141. This integrated circuit has an on-chip read-only memory which can store a "control program". An advance over the Am29PL141 is described in the related, co-pending application "Programmable, Expandable Controller With Flexible I/O" and such description is incorporated by reference herein. In one aspect of this invention, the advance includes the provision of an on-chip memory which is a random access memory (RAM) type. The RAM is used to store "microinstructions" which form a control program for the sequencer. In this sequencer, the control program can be dynamically altered which provides some external control over the sequencer.
Ideally, the sequencer should be accessible to an external microprocessor so that a wide variety of status conditions can be monitored by the microprocessor. Changes in the control program can then be dynamically made based on these status conditions internal to the sequencer as well as conditions external to the sequencer which are sensed by the microprocessor.
An interface, preferably integral to the integrated circuit housing the sequencer, should enable one of a number of commonly-used microprocessors to be connected to the integrated circuit.